System and method for marking an anatomical structure in three-dimensional coordinate system

ABSTRACT

The present invention is a device localization system that uses one or more ultrasound reference catheters to establish a fixed three-dimensional coordinate system within a patient&#39;s heart using principles of triangulation. The coordinate system is represented graphically in three-dimensions on a video monitor and aids the clinician in guiding other medical devices, which are provided with ultrasound transducers, through the body to locations at which they are needed to perform clinical procedures. In one embodiment of a system according to the present invention, the system is used in the heart to help the physician guide mapping catheters for measuring electrical activity, and ablation catheters for ablating selected regions of cardiac tissue, to desired locations within the heart.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 10/273,468, filed Oct. 21, 2002, which is a continuation of U.S.application Ser. No. 08/905,090, filed on Aug. 1, 1997, now U.S. Pat.No. 6,490,474, the disclosures of which are expressly incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of ultrasoundtracking systems. More specifically, it relates to systems for trackingthe positions of devices within the human body.

BACKGROUND OF THE INVENTION

For certain types of minimally invasive medical procedures, endoscopicvisualization of the treatment site within the body is unavailable ordoes not assist the clinician in guiding the needed medical devices tothe treatment site.

Examples of such procedures are those used to diagnose and treatsupra-ventricular tachycardia (SVT), atrial fibrillation (AF), atrialflutter (AFL) and ventricular tachycardia (VT). SVT, AFL, AF and VT areconditions in the heart which cause abnormal electrical signals to begenerated in the endocardial tissue to cause irregular beating of theheart.

A procedure for diagnosing and treating SVT or VT involves measuring theelectrical activity of the heart using an electrophysiology catheterintroduced into the heart via the patient's vasculature. The cathetercarries mapping electrodes which are positioned within the heart andused to measure electrical activity. The position of the catheter withinthe heart is ascertained using fluoroscopic images. A map of themeasured activity is created based on the fluoroscopic images and isshown on a graphical display. A physician uses the map to identify theregion of the endocardium which s/he believes to be the source of theabnormal electrical activity. An ablation catheter is then insertedthrough the patient's vasculature and into the heart where it is used toablate the region identified by the physician.

To treat atrial fibrillation (AF), an ablation catheter is maneuveredinto the right or left atrium where it is used to create elongatedablation lesions in the heart. These lesions are intended to stop theirregular beating of the heart by creating non-conductive barriersbetween regions of the atria. These barriers halt passage through theheart of the abnormal electrical activity generated by the endocardium.Following the ablation procedure, a mapping catheter is positioned inthe heart where it is used to measure the electrical activity within theatria so that the physician may evaluate whether additional lesions areneeded to form a sufficient line of block against passage of abnormalcurrents. S/he may also attempt to induce atrial fibrillation using apacing electrode, and then further evaluate the line of block byanalyzing the time required for the induced electrical activity to passfrom one side of the block to the other.

The procedures used to diagnose and treat SVT, VT, AFL and AF utilizecatheters which are maneuvered within the heart under fluoroscopy.Because the fluoroscopic image is in two-dimensions and has fairly poorresolution, it may be difficult for the physician to be certain of thecatheter positions. Thus, for example, once a physician has identifiedan area which is to be ablated (using a map of the measured electricalactivity of the heart) it may be difficult to navigate an ablationcatheter to the appropriate location in order to accurately ablate thearea of concern. It is therefore desirable to provide a system by whichthe positions of medical devices such as mapping and ablation cathetersmay be accurately guided to selected regions of the body.

Prior art tracking devices of the type which may track the positions ofmedical devices are described in U.S. Pat. No. 5,515,853 (Smith et al)and U.S. Pat. No. 5,546,951 (Ben Haim). While useful, neither of thedisclosed systems provides for determining medical device locationsrelative to a fixed coordinate system within the body. The lack of afixed coordinate system within the body can lead to tracking errorswhich in turn render it difficult to guide medical devices to thedesired locations within the body.

It is therefore desirable to provide an ultrasound tracking system formedical devices which permits the tracking of devices relative to afixed internal coordinate system. The system according to the presentinvention meets this objective as well as many others which enhance theaccuracy and usefulness of the tracking system.

SUMMARY OF THE INVENTION

The present invention is a device localization system that uses one ormore ultrasound reference catheters to establish a fixedthree-dimensional coordinate system within a patient's heart, preferablyusing principles of triangulation. The coordinate system is representedgraphically in three-dimensions on a video monitor and aids theclinician in guiding other medical devices, which also carry ultrasoundtransducers, through the body to locations at which they are needed toperform clinical procedures. In one embodiment of a system according tothe present invention, the system is used in the heart to help thephysician guide mapping catheters for measuring electrical activity, andablation catheters for ablating selected regions of cardiac tissue, todesired locations within the heart.

Three-dimensional images are shown on a video display which representthe three-dimensional positions and orientations of at least portions ofthe medical devices used with the system, such as the referencecatheter, and the electrodes of the mapping catheter and ablationcatheter. The video display may additionally include representations ofthe electrical activity measured by each mapping electrode at itsrespective location on the three-dimensional display. It may alsorepresent ablation lesions formed within the body at the appropriatethree-dimensional locations, and/or certain anatomic structures whichmay facilitate navigation of the medical device(s) within the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the system according to thepresent invention, showing the major components of the system.

FIG. 2 is a schematic representation of a three-dimensional coordinatesystem established using a reference catheter according to the presentinvention.

FIG. 3 is a side elevation view of a reference catheter for use with thesystem according to the present invention.

FIG. 4 is a side elevation view of a first alternative embodiment of areference catheter for use with the system according to the presentinvention, in which ultrasound transducers are included on a catheter ofa type conventionally used in the RV apex.

FIG. 5 is a side elevation view of a second alternative embodiment of areference catheter for use with the system according to the presentinvention, in which ultrasound transducers are included on a catheter ofa type conventionally used in the coronary sinus.

FIG. 6 is a perspective view of a piezoelectric cylinder of a type whichmay be used on catheters according to the present invention, includingthose shown in FIGS. 3-5.

FIG. 7 is a side elevation view of the piezoelectric cylinder of FIG. 6mounted on a catheter and modified to include a divergent lens.

FIG. 8 is a perspective view of a mandrel having a polymer piezoelectricwrapped around it for use with a reference catheter according to thepresent invention.

FIG. 9 is a side elevation view of a catheter for use with the system ofthe present invention which is provided with marking and ablationcapabilities.

FIG. 10 is a perspective view of a first alternative embodiment of acatheter with marking and ablation capabilities according to the presentinvention.

FIGS. 11 and 12 are side section views of second and third alternativeembodiments of catheters having marking and ablation capabilitiesaccording to the present invention.

FIG. 13 is a side elevation view of a mapping catheter for use with thesystem of the present invention. As with all of the catheters shownherein, the sizes of the electrodes and transducers are exaggerated forpurposes of illustration.

FIG. 14A is a front elevation view of the mapping catheter of FIG. 13,showing the spacing of the basket arms.

FIG. 14B is a view similar to the view of FIG. 14A showing alternatebasket arm spacing.

FIG. 15 is a cross-section view of the mapping catheter taken along theplane designated 15-15 in FIG. 13.

FIG. 16 is a plan view of an arm of the mapping catheter of FIG. 13.

FIG. 17 is a cross-section view of the arm of FIG. 16, taken along theplane designated 17-17.

FIG. 18 is a side elevation view of a linear lesion catheter for use inthe system according to the present invention.

FIG. 19 is a side section view of the linear lesion catheter of FIG. 18.

FIG. 20 is a cross-section view taken along the plane designated 20-20in FIG. 19.

FIG. 21 is a cross-section view taken along the plane designated 21-21in FIG. 19.

FIG. 22 is a cross-section view taken along the plane designated 22-22in FIG. 19.

FIG. 23 is a side section view, similar to the view of FIG. 19, of analternative embodiment of a linear lesion catheter for use with thesystem of the present invention.

FIG. 24 is a cross-section view taken along the plane designated 24-24in FIG. 23.

FIG. 25 is a side section view, similar to the view of FIG. 19, of analternative embodiment of a linear lesion catheter for use with thesystem of the present invention.

FIG. 26 is a cross-section view taken along the plane designated 26-26in FIG. 25.

FIG. 27A is a schematic drawing showing ultrasound ranging hardware andits interaction with the ultrasound hardware control and timing systems.

FIG. 27B is a schematic diagram illustrating in greater detailultrasound ranging hardware and ultrasound hardware control and timingsystems of the type shown in FIG. 27A.

FIG. 28A is a plot of the voltage over time on an ultrasound transmitline following initiation of a transmit pulse, and illustrates theringing which occurs on the transmit line following the transmit pulse.

FIG. 28B is a plot of the voltage over time on an ultrasound receiveline which is located near the transmit line at the time the transmitpulse of FIG. 28A is initiated. The figure shows the ringing whichresults from the ringing on the transmit line, and also shows a receivepulse following the ringing.

FIG. 28C is a plot of the voltage over time on an ultrasound receiveline which is located very close to a transmit wire at the time thetransmit pulse of FIG. 28A is instituted, and it illustrates that thereceive pulse may be lost in the ringing.

FIG. 28D is a plot of the voltage over time on an ultrasound transmitline which is short circuited immediately following the initiation of atransmit pulse.

FIG. 28E is a plot of the voltage over time on an ultrasound receiveline which is adjacent to the transmit line represented in FIG. 28D. Thefigure shows that ringing is eliminated on the receive line when thetransmit line is short circuited just after the transmit pulse is sent.

FIG. 29 is a schematic diagram illustrating a pulse generator circuitwhich includes a switch for short circuiting the transmit line justafter the transmit pulse is sent.

FIG. 30A is a schematic illustration of the sample and hold system usedfor gating position information to the cardiac cycle.

FIG. 30B shows an EKG plot together with a plot of transducercoordinates and illustrates a sample and hold sequence which takestransducer coordinates at the end of diastole.

FIGS. 31 and 32 illustrate the graphical user interface of the systemaccording to the present invention. FIG. 31 illustrates display ofanatomical features, reference catheters, a linear lesion catheter, andburns formed in the heart using the linear lesion catheter. FIG. 32illustrates display of the reference catheters, anatomical features,burns formed in the heart, and a basket catheter together with itsmapping electrode positions.

FIG. 33 is a flow diagram illustrating use of the catheters of FIGS. 3,9 and 13 to treat ventricular tachycardia.

FIGS. 34A-34C are a series of views of a heart illustrating certain ofthe steps of FIG. 33: FIG. 34A is an anterior section view of the heartshowing placement of a reference catheter in the right ventricle and amarking catheter in the left ventricle. FIG. 34B is a lateral view ofthe heart showing a reference catheter in the coronary sinus. FIG. 34Cis an anterior section view of the heart showing a reference catheter inthe right ventricle and a mapping catheter in the left ventricle. FIG.34D is a view similar to the view of FIG. 34C showing introduction of anablation catheter into the mapping catheter.

FIG. 35 is a flow diagram illustrating use of the system according tothe present invention together with the catheters of FIGS. 3, 9, 13 and18 to treat atrial fibrillation.

FIGS. 36A-36C are a series of views of a heart illustrating certain ofthe steps of FIG. 35: FIG. 36A is an anterior section view of the heartshowing placement of a reference catheter in the RV apex and a markingcatheter in left atria; FIG. 36B is an anterior section view of theheart showing a linear lesion ablation catheter in the left atria; FIG.36C is an anterior section view of the heart showing a mapping catheterin the left atria.

DETAILED DESCRIPTION

Localization System Overview

The localization system and procedure will next be described in generalterms. Specific examples of procedures which may be carried out usingthe system will be described in the Operation section of thisdescription. The system is described primarily with respect to cathetersin the heart, but it should be understood that the system is intendedfor use with other medical devices and in other regions of the body aswell.

Referring to FIG. 1, the present invention is a device localizationsystem 100 that uses one or more ultrasound reference catheters 10 toestablish a three-dimensional coordinate system within a patient'sheart. The system allows the positions of one or more additionalcatheters 12, 14, 16, to be represented graphically on a graphical userinterface 124 relative to a coordinate system. This aids the clinicianin guiding the additional catheter(s) 12, 14, 16 through the heart tolocations at which they are needed to perform clinical procedures.

In one embodiment of a system according to the present invention, theadditional catheters include mapping catheters 14 for measuringelectrical activity within the heart and ablation catheters 12, 16 forablating selected regions of cardiac tissue. These catheters 12-16 mayalso be described as “electrophysiology catheters” or “MEP catheters.”

Each of the reference catheters 10 carries a plurality of ultrasoundtransducers, with there being a total of at least four such transducersemployed during use of the system. The reference catheter transducerscan function as ultrasound receivers by converting acoustic pressure tovoltage, and as ultrasound transmitters by converting voltage toacoustic pressure. Each of the additional catheters 12, 14, 16 carriesat least one ultrasound transducer which preferably functions as anultrasound receiver but which may also function as a transmitter or atransmitter/receiver.

Using known techniques, the distance between each transducer and otherones of the transducers may be computed by measuring the respective timefor an ultrasound pulse to travel from a transmitting transducer to eachreceiving transducer. These distance measurements are preferably carriedout in parallel. In other words, when an ultrasound pulse is emitted bya reference catheter transducer, the system simultaneously measures therespective times it takes for the pulse to reach each of the othertransducers being used in the system.

The velocity of an acoustic signal in the heart is approximately1570-1580 mm/msec, with very small variations caused by blood andtissue. The time for an acoustic pulse to travel from one transducer toanother may therefore be converted to the distance between thetransducers by multiplying the time of flight by the velocity of anacoustic pulse in the heart (i.e. by 1570-1580 mm/msec). As detailedbelow, the system of the present invention uses this “time of flight”principal in combination with the geometric principal of triangulationto establish a three-dimensional coordinate system using the referencetransducers on the reference catheter 10, and to then use the additionalcatheter transducers to track the location of an additional catheter 12,14, 16, relative to the coordinate system.

During use of the system of the invention, one or more of the referencecatheters 10 is introduced into the heart or the surrounding vasculature(or even into other areas such as the esophagus) and is left in placefor the duration of the procedure. Once reference catheter(s) 10 arepositioned within or near a patient's heart, the system first measuresthe distances between each of the reference catheter transducers usingthe “time of flight” principal. It then uses these distances toestablish the relative positions of the reference transducers andtherefore to establish a three-dimensional coordinate system.

Referring to FIG. 2, establishing the coordinate system requiresplacement of the reference catheter(s) 10 such that at least fourreference transducers, designated T_(REF1) through T_(REF4) in FIG. 2,are available to define a 3-dimensional coordinate system as follows:T_(REF1) through T_(REF3), define the plane P at z=0; one referencetransducer T_(REF1) defines the origin of the coordinate system; a linebetween T_(REF1) and T_(REF2) defines the x-axis of the system; andT_(REF3) lies in the plane z=0. The fourth reference transducer,T_(REF4), lies on one side of the plane P, at z>0. Given theseconstraints, the coordinates of the reference transducers can becomputed using the law of cosines. See, for example, AdvancedMathematics, A preparation for calculus, 2nd Ed., Coxford, A. F., PayneJ. N., Harcort Brace Jovanovich, New York, 1978, p. 160.

Each of the reference transducers T_(REF1) through T_(REF4) must becapable of both receiving and transmitting ultrasound pulses. Asdiscussed, each reference transducer is separately made to emit acousticpulses that are received by each of the other reference transducers sothat the distances d1 through d6 shown in FIG. 2 are calculated usingthe respective times it takes for an acoustic pulse to travel betweeneach pair of the reference transducers. These distances are triangulatedto establish the positions of the reference transducers relative to eachother, and therefore to establish a three-dimensional coordinate system.

Once a 3-dimensional coordinate system is established in the mannerdescribed, the three-dimensional location of an additional cathetertransducer placed near or within the heart (such as a transducer on amapping or ablation catheter 12, 14, or 16) can be calculated asfollows. First, using the “time of flight” method, the distances betweeneach of the reference transducers T_(REF1) through T_(REF4) and theadditional catheter transducer (designated T_(CATH) in FIG. 2) areestablished, in parallel. In practice, these distances are preferablyalso performed in parallel with the distance measurements that are madeto establish the coordinate system. Next, using basic algebra and thelaw of cosines (see, e.g., the Advanced Mathematics text cited above),the coordinates of T_(CATH) relative to the reference transducers arecalculated using the measured distances from T_(REF1) through T_(REF4)to T_(CATH). This process is referred to as triangulation.

The locations of all or portions of the reference catheters may bedisplayed as well. The system is preferably programmed to extrapolatecatheter position from the coordinates of the transducer locations basedon models of the various catheters pre-programmed into the system, andto display each catheter's position and orientation on a graphical userdisplay (see display 124 in FIG. 1). The locations of all or portions ofthe additional catheters (such as, for example, their distal tips, theirelectrodes or ablation sections, if any, or other sections which may beof interest) are displayed.

The reference catheter(s) 10 thereby establish an internal coordinatesystem by which the relative positions of EP catheter transducers in theheart may be calculated using triangulation and shown in real-time on athree dimensional display.

Ultrasound Catheters

Catheters of the type which may be used with the system according to thepresent invention are shown in FIGS. 3, 9, 13 and 18. These include areference catheter 10 (FIG. 2), a marking and ablation catheter 12 (FIG.9), a basket-type mapping catheter 14 (FIG. 13), and a linear lesionablation catheter 16 (FIG. 18).

Reference Catheters

Referring to FIG. 3, a reference catheter 10 according to the presentinvention is an elongate catheter having a plurality of ultrasoundtransducers 18 positioned at its distal end. The transducers 18 arepiezoelectric transducers capable of transmitting and receivingultrasound signals.

The reference catheters can be integrated with typical EP catheters byproviding the ultrasound transducers described above.

This allows the system to utilize the localization function usingcatheters which are already needed for the EP procedure. Thus, use ofthe system does not require the physician to use more catheters thanwould be used had the EP procedure been carried out without thelocalization function.

For example, referring to FIG. 4, the reference catheter 10 a may be anRV apex catheter having a distal pair of EP electrodes 30, an ultrasoundtransducer 18 a at the distal tip, and additional ultrasound transducers18 proximally of the distal tip. It may also be a coronary sinusreference catheter 10 b (FIG. 5) having at least three bipole pairs ofEP electrodes 30 distributed over the section of the catheter that ispositioned in the coronary sinus, and having at least three ultrasoundtransducers also distributed over the section of the catheter that is inthe coronary sinus.

Referring to FIG. 6, a preferred transducer 18 is a piezoelectriccylindrical tube having inner and outer surfaces. The cylindricaltransducer may be made of PZT-5H, PZT-5A, PMN (lead metaniobate or leadmagnesium niobate) or other piezoelectric ceramic materials.

Electrodes 20 are positioned on the inner and outer surfaces of thetransducer. The electrodes are metal surfaces not limited to materialssuch as sputtered chrome and gold, electroless nickel, or fired silver.The piezoelectric ceramic is polarized in the thickness mode, i.e.,between the two electrodes 20.

The cylinder includes an outside diameter (designated “OD” in FIG. 6) ofapproximately 0.040 to 0.250 inches, and preferably approximately 0.060to 0.090 inches. The cylinder has a length L of approximately 0.020 to0.125 inches and preferably approximately 0.030 to 0.060 inches. Wallthickness W is approximately 0.004 to 0.030 inches and preferablyapproximately 0.006 inches to 0.015 inches. The transducers 18 arespaced from one another along the catheter 20 (FIG. 3) by a distance ofapproximately 0.5-10 cm, and most preferably 1-3 cm.

Preferably, the localization system is operated using the same operatingfrequencies for all transducers. The optimal operating frequency for thesystem is determined by considering the resonant frequencies of theultrasound transducers used for the catheters in the system. It has beenfound that, given the dimensions and thus the resonances of thepreferred transducers being used in the system, the transducers are mostpreferably operated at a frequency of approximately 1.0-3.0 MHz, whichin the case of the transducer 18 is the transducer resonance in thelength mode. Transducer 18 further has a beam width of approximately114°, where the beam width is defined as the angle over which the signalamplitude does not drop below 6 dB from the peak amplitude. If desired,a diverging lens 22 (FIG. 7), in the form of a spherical bead of epoxyor other material may be formed over the ceramic cylinder to make thesignal strength more uniform over the beam width.

Referring to FIG. 8, the reference catheter transducers 18 b mayalternatively be formed of piezoelectric polymer films of copolymerssuch as PVDF. Such films would have thicknesses of approximately0.005-1.0 mm, and preferably approximately 0.007-0.100 mm, and wouldpreferably include gold film electrodes on the inner and outer surfaces.As shown in FIG. 8, the polymer film would be wrapped around a mandrel24 (which may be part of the catheter shaft 10 c itself or a separatepolymer plug inside the catheter 10). A transducer configuration of thistype operates with a very large band width and does not have a specificresonance due to the polymer piezoelectric.

Electrode leads (not shown) are attached to the inner and outertransducer electrodes (such as electrodes 20 of FIG. 6). Ifpiezoelectric ceramics are used as in FIGS. 6 and 7, leads may beattached using low temperature solders which typically contain largeproportions of indium metal. Leads may alternatively be attached withsilver epoxy. It is important that the leads be attached using a minimumamount of material to minimize distortion of the acoustic field. In thecase of the polymer transducers of FIG. 8, photo lithographic techniquesare typically used to create electrodes and their associated lead tabs.In this manner, the one side electroded polymer at the tab site does notcontribute to the acoustic field. Leads are typically attached to thesetabs with either low temperature indium based solders or with silverepoxy. Therefore, for these polymer transducers, the amount of materialon the connection tab does not affect the acoustic field.

The reference catheter preferably includes at least four suchtransducers so that a three-dimensional coordinate system can beestablished using a single catheter. If desired, the reference cathetermay have more transducers or it may have fewer transducers if more thanone reference catheter is to be used to establish the three-dimensionalcoordinate system. Using more than four reference transducers isadvantageous in that it adds redundancy to the system and thus enhancesthe accuracy of the system. When more than four reference transducersare used, the problem of determining the location of cathetertransducers is over determined. The additional redundancy may providegreater accuracy if the measured distances between the referencetransducers and catheter transducers are noisy. The overdeterminedproblem can be solved using multi-dimensional scaling as described in“Use of Sonomicrometry and Multidimensional Scaling to Determine 3DCoordinates of Multiple Cardiac Locations: feasibility andimplementation”, Ratciffle et. al, IEEE Transactions BiomedicalEngineering, Vol. 42, no. 6, June 1995.

Referring again to FIG. 3, a connector 32 enables the catheter 10 to beelectrically coupled to the ultrasound ranging hardware 116 (describedbelow and shown in FIG. 1).

Four twisted pairs 26 of Teflon coated forty-two gauge copper wire (onepair can be seen in the cutout section shown in FIG. 3) extend fromconnector 32 through the catheter 10. Each twisted pair 26 iselectrically coupled to a corresponding one of the ultrasoundtransducers 18, with one wire from each pair 26 coupled to one of thetransducer electrodes 20 (FIG. 6). When a transducer is to act as anultrasound transmitter, a high voltage pulse (i.e, approximately10-200V) is applied across the corresponding twisted pair 21 and causesthe transducer 18 to generate an ultrasound pulse. When a transducer isto act as an ultrasound receiver, the ultrasound ranging hardware 116(FIGS. 27A-27B, described below) awaits receive pulses of approximately0.01-100 mV across the twisted pairs corresponding to receivingtransducers. Additional leads (not shown) couple the EP electrodes 30 tothe EP hardware 114 (FIG. 1).

To facilitate manipulation of the reference catheter through a patient'svessels and into the heart, the reference catheter 10 may have apre-shaped (e.g. curved) distal end.

Marking/Ablation Catheter

Referring to FIG. 9, the system of the present invention preferablyutilizes a catheter 12 to identify the locations of anatomical landmarks(such as the septal wall) relative to the coordinate system so that thelandmarks may be included on the three-dimensional display. Showinganatomical landmarks on the display correlates the three-dimensionalcoordinate system to discrete anatomical locations and thereby assiststhe physician in navigating EP catheters to the desired locations withinthe heart.

The marking catheter 12 is preferably a 7 French steerable catheterhaving one or more ultrasound transducer(s) 34 mounted at or near itsdistal tip. Preferably, the catheter 12 includes one transducer at ornear its distal tip and a second transducer spaced from the distal tipby approximately 0.5-4.0 cm. The marking catheter 12 need not be onewhich is limited to use in marking anatomical sites. It can be acatheter useful for other purposes as well; the term “marking catheter”is being used in this description as a matter of convenience. Catheter12 may also include an ablation electrode 36 at its distal tip, so thatit may also be used to ablate tissue while the position of the ablationelectrode 36 is tracked using the localization system 100. It may alsoinclude other electrophysiology electrodes 38 which may be used forpacing and/or mapping as desired by the user.

The transducers 34 may be similar to the reference catheter transducers18. While the outer diameter and wall thickness of the transducers 34may differ from that of transducer 18 to accommodate mountingrequirements, the length of the transducers 34 is preferably the same asthat of the transducers 18 to assure a common operating frequency ofapproximately 1.0-3.0 MHZ.

Alternatively, the more distal transducer might be packaged differentlythan the reference catheter transducers. For example, referring to FIG.10, the transducer 34 may be mounted just proximal of the distalablation tip 36. Alternatively, a cylindrical transducer 34 a or a platetransducer 34 b may be positioned inside the distal ablation tip, inFIGS. 11 and 12, respectively. An internal piezoelectric transducerwould be embedded in a bead of epoxy 40 positioned in the catheter tip.This bead would preferably have a spherical contour across the distalend so that it would act as a divergent lens for the ultrasound energy.The metal forming the ablation tip 36 must be very thin (i.e., less thana small fraction of a wavelength) to facilitate the transmission ofacoustic energy to and from an internal transducer.

The marking catheter 12 may additionally be provided with EP electrodes38. As shown in FIG. 9, a handle 42 and a knob 44 for actuating a pullwire (not shown) allow the marking catheter 12 to be maneuvered througha patient's vessels and heart using conventional steering mechanisms. Aconnector 46 enables the catheter 12 to be electrically coupled to theEP hardware 114 and the ultrasound ranging hardware 116 (describedbelow, see FIG. 1).

Mapping Catheter

FIG. 13 shows a first embodiment of a mapping catheter 14 for use withthe system according to the present invention. The catheter 14 is of thetype known in the art as a “basket” catheter. It includes an elongateshaft 48 carrying a mapping basket 50 at its distal end. The basket 50is formed of preferably eight arms 52. Arms 52 are constructed ofribbons of a shape memory material such as Nitinol. The shape memorymaterial is treated such that the ribbons assume the basket structureshown in FIG. 13 when in an unstressed condition.

The arms 52 may be concentrated at one section of the basket (FIG. 14A)so that during use mapping may be concentrated in one area of a cardiacchamber. The arms may alternatively be uniformly spaced as shown in FIG.14B. Basket catheters of these types are shown and described in U.S.Pat. No. 5,156,151, the disclosure of which is incorporated herein byreference.

A sheath 54 is disposed around shaft 48. Sheath 54 is longitudinallyslidable between the proximal position in FIG. 13 and a distal positionin which the basket 50 is compressed within it. During use the sheath 54is moved to the distal position to compress the basket before thecatheter 14 is inserted into the patient, so that the basket can beeasily moved through the patient's vessels and into the patient's heart.Once the basket is within the desired chamber of the patient's heart,the sheath is withdrawn, the basket is opened into its expandedcondition, (either by spring action of the arms 52 or by a separateactuator) and the arms to map electrical activity of the chamber wall.

Each arm 52 of the basket catheter 14 carries a plurality of EP mappingelectrodes 56 designed to detect the electrical activity of underlyingcardiac tissue. A plurality of ultrasound receiving transducers 58 arealso mounted to each arm 52. Preferably, the mapping electrodes 56 andthe ultrasound transducers 58 alternate with each other along the lengthof each arm 52, although there need not be one-to-one correspondencebetween the transducers and electrodes.

FIG. 16 is a plan view of one arm 52 of basket catheter 14, and FIG. 17is a side section view of the arm of FIG. 16. As shown, the mappingelectrodes 56 and ultrasound transducers 58 are preferably formed on aflex circuit 60 which is attached to the arm 52. Copper leads 62 areformed on the flex circuit and each lead is electrically connected toone of the EP electrodes 56 and one of the ultrasound transducers 58,and to the EP and localization hardware 110 (FIG. 1). Each arm 52,including its associated flex circuit 60, is covered in polyethyleneshrink tubing 64, with only the electrodes 56 being exposed through theshrink tubing 64.

Referring to FIG. 16, a preferred piezoelectric transducer for themapping catheter comprises a flat piezoelectric ceramic plate 66. Theplate 66 may be made of PZT-5H, PZT-5A, PMN (lead metaniobate or leadmagnesium niobate) or other piezoelectric materials.

The transducer includes a depth D and length L, each of approximately0.010 to 0.060 inches, and preferably approximately 0.025 to 0.040inches. The transducer has a wall thickness W of approximately 0.004 to0.030 inches and preferably approximately 0.006 to 0.015 inches. Thelength and depth resonances of the transducer fall in the range from 1.0MHz to 3 MHz and thus contribute to the overall performance of thesystem. The beam width considerations are the same as those describedabove for the reference catheter transducers 18 (FIG. 6).

Electrodes 68 a, 68 b are positioned on the upper and lower flatsurfaces of the plate. The electrodes are metal surfaces not limited tomaterials such as sputtered chrome and gold, electroless nickel, orfired silver. The piezoelectric ceramic is polarized in the thicknessmode, i.e., between the two electrodes.

The mapping catheter transducers 58 may alternatively be formed ofpiezoelectric polymer films of copolymers such as PVDF. Such films wouldhave thicknesses of approximately 0.005-1.0 mm, and preferablyapproximately 0.007-0.100 mm, and would preferably include gold filmelectrodes on the inner and outer surfaces. The polymer film wouldpreferably be taped to the printed wiring board of the basket arm, andleads attached to the top electrodes in a manner similar to thatmentioned above for the reference catheter transducers. Alternatively,the polymer film could be used to form the entire flex circuit.

Lead wires 70 a, 70 b extend between the copper leads 62 and theelectrodes 68 a, 68 b. It is important to note that each of the leads 62electrically connects both an ultrasound transducer 58 and an EPelectrode 56 to the EP and localization hardware 110. Each lead 62therefore carries electrical activity measured by EP electrodes 56 aswell as receive signals from the ultrasound transducers 58 to thehardware 110. It is possible to do this because EP signals have a lowerfrequency (i.e., on the order of 1 Hz-3 kHz) than the ultrasonicsignals, which have frequencies of approximately 500 kHz-30 MHz. Thus,the EP signals can be removed from the recorded signal using low-passfiltering while the ultrasound signal can be removed using high passfiltering.

Combining EP and ultrasound signals on the same lead 62 has theadvantage of reducing the total number of conductors in the catheter 14.While this is advantageous, it is not a requirement for functionality ofthe system. Naturally, the system may also be provided using separateleads for the EP and ultrasound signals.

For both piezoelectric ceramic and polymer transducers, one lead 70 bwill most typically be attached by bonding the bottom electrode 68 b ofthe piezoelectric (e.g., plate 66) with silver epoxy to the printedcircuit of the basket arm. Leads 70 a may be attached to the topelectrodes 68 a in a manner similar to that set forth with respect tothe reference catheter transducers. For the piezoelectric ceramics 66,the top lead 70 a may be attached with low temperature solders whichtypically contain large proportions of indium metal. It is importantthat the leads be attached using a minimum amount of material tominimize distortion of the acoustic field. Top leads 70 a may also beattached with silver epoxy. In the case of the polymer piezoelectrics,metallization of the electrodes and leads is typically achieved usingphoto lithographic techniques. In this manner, the one side electrodedpolymer at the lead site does not contribute to the acoustic field asdiscussed previously for the polymer transducer of the referencecatheter.

Acoustic wave propagation does not occur across a vacuum or air gap,consequently it is necessary to provide a rubber path or a path throughan insulating polymer in order to fill air gaps around the transducers.For example, after the top lead 70 a has been attached, the entire topsurface and surrounding areas including the inner surface of the shrinktubing is coated with a rubber primer. Subsequently, the area betweenand around the top surface of the piezoelectric and the shrink tubing isfilled with a silicone rubber material.

Alternatively, the top surface of the piezoelectric and the electricallead may be coated with an insulating polymer. After the heat shrinktubing is attached to the basket strut, a small area over and around thetop electrode of the ceramic may be cut out of the shrink tubing toprovide an unobstructed exposure of the transducer to the blood field.

The EP electrodes 56 are preferably platinum black electrodes having asize of approximately 0.009×0.030 inches. For these small electrodes,platinum black is used for low impedance, i.e., approximately less than5.0 k Ohms over the frequency range (approximately 1 Hz-3 kHz) ofinterest for EP signals. This is important in that it prevents theimpedance of the ultrasound transducers from loading the output of theEP electrodes.

FIG. 15 is a cross-section view of the portion of the catheter 14 whichis proximal of the basket 50. The catheter shaft 48 is formed of aninner shaft 72 and an outer, braided shaft 74 preferably made fromstainless steel braid of a type conventionally known in the art. Theinclusion of the braid improves the torque characteristics of the shaft48 and thus makes the shaft 48 easier to maneuver through patient'svessels and heart.

Inner shaft 72 includes a center lumen 76 through which ribbon cables 78extend. Leads (not shown) are formed on the ribbon cables 78 andfunction to carry signals corresponding to signals received by theultrasound transducers 58 and by the electrophysiology electrodes 56 tothe system hardware 110 (FIG. 1). An ablation catheter lumen 80 extendsthrough the shaft 48 and allows an ablation catheter such as catheter 12to be introduced through the shaft 48 and into contact with tissuesurrounding the basket 50.

Inner shaft 72 further includes a deflection lumen 82. A pull wire (notshown) extends through the deflection lumen 82 and facilitates steeringof the basket using means that are conventional in the art.

Linear Lesion Ablation Catheter

FIGS. 18 through 26 show a linear lesion ablation catheter 16 for usewith the system 100 of the present invention. Catheter 16 is an elongateshaft preferably constructed of a thermoplastic polymer, polyamid ether,polyurethane or other material having similar properties. An ablationsection 84, the section of the catheter 16 at which ablation is carriedout, is located at the distal end of the shaft.

As shown in FIG. 18, an elongate window 86 is formed in the wall of theablation section 84. The window 86 may be made from heat shrinkpolyethylene, silicone, or other polymeric material having a pluralityof small holes or perforations formed in it. It may alternatively beformed of the same material as the remainder of the shaft and simplyinclude a plurality of holes formed through it.

Referring to FIG. 19, a foam block 88 is disposed within the catheter,next to the window 86. The foam block 88 is formed of open cellpolyurethane, cotton-like material, open-cell sponge, hydrogels, orother foam-like materials or materials that are permeable by conductivefluids. A plurality of RF ablation electrodes 90 line the edge of thefoam block 88 such that the foam block lies between the electrodes 90and the window 86.

Ultrasound transducers 92 are positioned at the distal and proximal endsof the foam block 88. The transducers 92 are preferably formed ofpiezoelectric ceramic rings having electrodes bonded to their inner andouter surfaces, although the transducers may also be formed in a varietyof alternative shapes.

Referring to FIGS. 20-22, several lumen extend through the catheter 16.The first is a fluid lumen 94 that extends the length of the catheter 16and is fluidly coupled to a fluid port 96 (FIG. 18) at the proximal endof the catheter. It should be noted, with reference to FIG. 20, that thewalls of the fluid lumen are cut away at the ablation section 84 toaccommodate placement of the foam block 88 and the RF electrodes 90within the catheter.

A pair of lead lumen 98 house lead wires 100 that carry RF energy to theelectrodes 90 and lead wires 102 that carry voltage signals from thetransducers 92. A fourth lumen 104 houses a Nitinol core wire 106 whichprovides rigidity to the catheter.

Because breaks in a linear lesion can reduce the success of an ablationprocedure by leaving a path through which current may travel duringatrial fibrillation episodes, the fluid lumen, foam, and window areprovided to improve the coupling of the RF energy to the cardiac tissueto minimize the likelihood of breaks in the lesion.

Specifically, during use, the window 86 of ablation section 84 of theapparatus is positioned adjacent to the body tissue that is to beablated. RF energy is delivered to the electrodes 90 while saline orother conductive fluid is simultaneously delivered through the fluidlumen 94. The conductive fluid passes out of the fluid lumen 94 and intothe foam 88, and contacts the electrodes 90. The fluid also flowsthrough the window 86 into contact with the body tissue, therebyimproving the coupling of the RF energy from the electrodes 90 to thetissue and improving the efficiency of the ablation of the tissue.

Using a conductive liquid dispersed over the desired area as a mechanismfor coupling RF energy to the tissue produces lesions having greatercontinuity (and thus fewer breaks through which current can pass duringatrial fibrillation episodes) than lesions formed by apparatuses thatrely solely on direct contact between the electrodes and the bodytissues, decreasing the likelihood of thrombus formation on theelectrodes and thus decreasing the chance of an embolism. The foam andthe window improve ablation in that the conductive liquid is uniformlydispersed within the foam and then is focused onto the body tissue as itpasses through the holes or pores in the window. This concept, andseveral alternate ways of configuring linear lesion catheters that maybe adapted to include ultrasound transducers and used in the system ofthe present invention, are described in published InternationalApplication PCT/US96/17536, the disclosure of which is incorporatedherein by reference.

FIGS. 23 and 24 show a first alternative embodiment of a linear lesioncatheter according to the present invention. The first alternativeembodiment 16 a differs from the embodiment of FIG. 19 primarily in theshape and placement of the transducers. Transducers 92 a of the firstalternative embodiment are piezoelectric chips embedded within the foamblock 88. Each transducer 92 a includes a pair of electrodes on itsopposite faces and is encapsulated in an insulating cocoon 108 of epoxy,acrylic, or silicone rubber which prevents the fluid in the foam fromcreating a short circuit between the electrodes.

A second alternative embodiment of a linear lesion catheter according tothe present invention is shown in FIGS. 25 and 26. The secondalternative embodiment also differs from the preferred embodiment onlyin the form and placement of the transducers. Each transducer 92 b andits leads 102 b is inside an epoxy capsule 109 embedded in the foamblock 88. It should be noted, then, that only the RF electrode leads 100extend through the lumen 98. The leads 102 b of the second alternativeembodiment extend through fluid lumen 94 as shown.

System Components

Referring to FIG. 1, the system 100 generally includes amplification andlocalization hardware 110, catheters 10, 12, 14 and 16, and amicroprocessor workstation 112.

Hardware 110 includes conventional signal amplifiers 114 of the typeused for electrophysiology procedures (for example, the Model 8100/8300Arrhythmia Mapping System available from Cardiac Pathways Corporation,Sunnyvale, Calif.). It also includes ultrasound ranging hardware 116 andan ultrasound hardware control and timing component 118 which togetherinitiate, detect, and measure the time of flight of ultrasound pulsesemitted and received from the ultrasound transducers on the referenceand EP catheters 10-16.

Signal amplifiers 114 and the ranging hardware 116 and controller 118are electronically coupled to a microprocessor workstation 112. Themicroprocessor work station 112 is designed to control the systemhardware and the data processing for both the EP and ultrasoundfunctions of the system, and to generate a visual display of EP andcatheter position data for use by the clinician.

For EP functions, the microprocessor 112 includes an amplifiercontroller 120 that delivers mapping, and/or pacing commands to the EPsignal amplifiers 114. Signal processors 122 receive data correspondingto electrical activity measured by the mapping catheters 14, 16 andgenerate graphical representations of the measured data for display ongraphical interface display 124. The mapping signals shown on thegraphical display can represent any number of parameters orcharacteristics, such as measured signal values or impedance values,indicators of electrode contact, or indicators of the probability thatthere is an arrhythmogenic site in the area, etc.

Ultrasound hardware controller 118 and a triangulation processor 126control the catheter localization functions and data processing. Duringuse, controller 118 directs the ultrasound ranging hardware 116 toinitiate an ultrasound pulse from a selected transmitting transducer. Itfurther directs the hardware 116 to (1) detect, in parallel, voltagescorresponding to reception of the ultrasound pulse by the receivingtransducers, and (2) measure the elapsed time (time of flight) betweentransmission of the ultrasound pulse and its detection by the selectedreceiving transducers. Triangulation processor 126 receives datacorresponding to these time of flight measurements from the ranginghardware 116 and uses it to calculate the locations of the EP cathetertransducers relative to the reference transducers (see LocalizationSystem Overview). Data corresponding to catheter position, as calculatedfrom transducer locations, and measured EP signals is shown in graphicalform on graphical user interface display 124.

The ultrasound ranging hardware 116 may be configured to detect anacoustic pulse received by a receiving transducer in a number of ways.For example, if the transmitting transducer is made to generate a shortburst of high frequency ultrasound energy, the hardware 116 may beconfigured to detect the first signal excursion above or below apredetermined maximum and minimum voltage threshold, or the peak of areceived signal. Alternatively, the transducer may be made to generate acontinuous wave of low frequency ultrasound, in which case the hardware116 would be configured to measure the difference in phase between thestanding wave as generated by the transmitting transducer and asdetected by the receiving transducer.

Referring to FIG. 27A, the ultrasound ranging hardware 116 includes aplurality of channels 128 a, 128 b, each of which is electronicallycoupled to one of the ultrasound transducers in the system. Depending onwhether a transducer is intended to transmit and receive ultrasoundsignals (as in the case of a reference catheter transducer 18) or toreceive ultrasound signals only (as in the case of an additionalcatheter transducer 34, 58 or 92), a transducer's corresponding channelcircuitry may be configured to permit transmission and receipt ofultrasound signals by the transducer, or it may be configured only toallow receipt of signals by the transducer. Accordingly,transmit/receive channels 128 a are each connected to a correspondingone of the reference catheter transducers 18 (FIG. 3), and receivechannels 128 b are each connected to a catheter transducer 34, 58, 92(e.g., FIGS. 9, 13 and 19).

Referring to FIG. 27B, the circuitry of each of the channels 128 a, 128b generates digital data corresponding to the time of flight of anultrasound transmit pulse from a transmitting transducer to thetransducers corresponding to each of the channels 128 a, 128 b. Eachchannel 128 a, 128 b includes an amplifier 130 which amplifies voltagesignals generated by the ultrasound transducers in response to receivepulses. The transmit/receive channels 128 a additionally includetransmitters 132 which, in response to signals from transmit and receivecontroller 142 (discussed below), apply voltages across the referencetransducers 18 to trigger ultrasound pulses.

Each channel 128 a, 128 b further includes a threshold detector 134which triggers a latch 136 once a received signal exceeds a thresholdlevel. Latch 136 is coupled to distance register 138 which is in turncoupled to place distance output data onto data bus 140 upon activationof the latch 136.

Ultrasound hardware control and timing component 118 includes transmitand receive controller 142. Controller 142 is electronically coupled toa system clock 141 that drives a distance counter 144, and to athreshold amplitude generator 146 which provides the threshold referenceinput for threshold detectors 134.

As will be discussed in greater detail, count values from the distancecounter 144 are used by the system of the invention to calculate thedistances between transmitting transducers and receiving transducers.Because system clock 141 drives the distance counter 144, it is thefrequency of the system clock that determines the resolution of measureddistances between transducers. The higher the frequency of the clock,the greater the resolution of the distance measured. Clock 141 istherefore a high frequency counter which preferably operates at leastapproximately 5-50 MHz, which is equivalent to a resolution ofapproximately 0.3-0.03 mm.

The threshold amplitude generator 146 produces time varying positive andnegative thresholds that are used as inputs to the threshold detectors134 of each channel 128 a, 128 b. Preferably, one threshold amplitudegenerator 146 is used for the entire system in order to minimize theamount of hardware in the system. However, the system may alternativelyuse a separate threshold amplitude generator for each channel, orseparate threshold amplitude generators for different groups ofchannels. For example, different threshold amplitude generators may beused for different types of receiving transducers, since some produceweaker signals and therefore require lower thresholds. As anotheralternative, a fixed threshold may be used together with a variable gainamplifier in place of amplifier 130.

The threshold amplitudes are preferably varied by the thresholdamplitude generator 146 so that they are large at the time a transmitpulse is initiated and so that they decrease as time passes followingtransmission of a pulse. Using a variable threshold rather than a fixedone is beneficial because the dynamic range (i.e., the ratio of thelargest signal to be detected to the smallest signal to be detected) isquite large, and may even be as high as 70 dB due to factors such asanisotropy of the transit and receive beam profiles, signal decay due toultrasound wave propagation, and attenuation of the signal caused byblood and tissue. Because transducer receiving wires for a catheterbased system must be closely spaced, a fixed dynamic range of thismagnitude could lead to erroneous data, because cross-talk between theclosely spaced receiving wires could be interpreted by the system to beactual receive signals.

It should be noted that both positive and negative thresholds are usedso as to increase the accuracy of the detection time, since a negativeoscillation of a transmit pulse may reach the detection threshold beforea positive oscillation. Latch 136 will therefore be triggered bywhichever of the positive or negative thresholds is achieved first.

When a transmit pulse T (FIG. 28A) is being sent to a transducer,oscillation, or “ringing”, designated “R_(T)”, can occur on thecorresponding twisted pair 26 (FIG. 3). The ringing in the transmit lineis not problematic in and of itself. However, in catheters such as thereference catheter 10 which includes transducers which can both transmitand receive ultrasound signals, the close proximity of the transmittingand receiving lines can cause the ringing to cross over to the receivingline. This problem arises most frequently when the system is computingthe relative orientations of the reference transducers 18 (FIG. 3) inorder to establish the three-dimensional coordinate system, since thatprocedure requires measuring the time it takes for a pulse emitted byone of the reference transducers 18 to be received by the otherreference transducers 18 on the same catheter. The ringing (which isdesignated “R_(R)” in FIGS. 28B and 28C) can be of similar magnitude toa receive signal “S” and can therefore make it difficult to determinewhether a receive signal has been detected.

If the transmitting and receiving transducers are far apart, a receivesignal on a receiving line (such as twisted pair 26) will be measured bythe ultrasound system circuitry despite the ringing, becausetransmission of the receive signal on the receiving line will happenonly after the ringing has diminished. See FIG. 28B. However, if thetransmitting and receiving transducers are close together (i.e.,separated by less than approximately 2 cm), the receive pulse will belost in the ringing on the receive line, because the receive pulse willreach the receiving line while the ringing is still occurring. See FIG.28C.

It has been found that this problem may be avoided by includingcircuitry which will short the conductors of the transmit lineimmediately after the transmit pulse is sent. An example of suchcircuitry is shown in FIG. 29. The circuit includes the pulse generator148 and center tapped transformer 150 which comprise basic pulsegenerating circuitry, plus a switch 152 which is closed immediatelyafter a transmit pulse in order to short the ringing to ground. A smallimpedance 154 is placed in series with the switch in order to dampen theringing through the short circuit. As illustrated in FIGS. 28D and 28E,by eliminating the ringing from the transmitting line, the switcheliminates the ringing from the receiving line as well.

Referring again to FIG. 27B, during use of the system, eachtransmit/receive channel 128 a is sequentially selected for transmissionof a transmit pulse, and all channels 128 a, 128 b are simultaneouslyselected for parallel reception of distance data. Transmit and receivecontroller 142 selects which of the transmit/receive channel 128 a willinitiate an ultrasound pulse, and cycles through each transmit/receivechannel, causing sequential transmission of pulses by the referencetransducers 18 (FIG. 3). It uses the system clock 141 to generate alower frequency transmit clock, which in turn controls how oftenultrasound pulses are transmitted.

Each time a transmit pulse is to be initiated, the transmit and receivecontroller 142 performs the following sequence of steps. The distancecounter 144 is first reset to zero, and the threshold amplitudegenerator 146 is reset. A detection hold off and reset signal is nextsent by controller 142 to all channels 128 a, 128 b. This resets thelatch 136 for each channel and prevents it from latching for a specifiedtime period to prevent detection due to electromagnetic coupling ofringing after transmission of a transmit pulse. This “hold off” periodis determined by the smallest distance within the patient that is to bemeasured, and is calculated according to the following equation:hold off period=smallest distance*1/(velocity of transmit signal).

Thus, if the smallest distance to be measured is 10 mm, the “hold offperiod” is:

${10\mspace{14mu}{mm}*\frac{1}{1.5\mspace{14mu}\frac{mm}{\mu sec}}} = {6.66\mspace{14mu}{\mu sec}}$

After the hold off and reset signals, a transmit control signal is sentto a selected one of the transmit/receive channels 128 a, causing it toinitiate a transmit pulse. Shortly afterwards, a signal is sent to thesame transmitter to initiate damping in order to prevent/reduce ringingas described above.

When a transmit pulse is initiated, the distance counter 144 issimultaneously activated. After a transmit pulse is triggered, eachchannel 128 a, 128 b “listens for” a receive pulse. When the thresholddetector 134 for a particular channel detects a receive pulse thatexceeds the threshold set by the threshold amplitude generator 146, thelatch 136 for that channel is activated. Once the latch 136 isactivated, a load data command is sent to the associated distanceregister 138 and the current contents of the distance counter 144 areloaded into the distance register 138 for that channel. This data issubsequently placed on the distance data bus 140 along with dataindicating which channel transmitted the pulse. Thus, the data busreceives a number of distance values which correspond to the number oftransmit/receive and receive only channels. These distance values arethen used by the triangulation processor 126 (FIG. 1) to determine therelative positions of the ultrasound transducers, and the microprocessor112 uses the position data to create a three-dimensional display of thecatheters.

Graphical Display Features

As described, the three-dimensional positions of the integratedultrasound transducers (such as those on catheters 10, 12, 14 and 16)may be continuously displayed in real-time on the graphical userinterface display 124 (FIG. 1). The three-dimensional positions of thecatheters (10, 12, 14 and 16), or portions thereof, may also oralternatively be continuously displayed based on the position of thetransducers by extrapolating the catheter position using a known modelof the catheter programmed into the system. The three-dimensionalpositions of the transducers and/or catheters may also be stored in thesystem's memory and selectively displayed on the graphical display userinterface display 124 as required during a procedure.

For example, data corresponding to electrode locations on a mappingbasket 14 may be saved in the system memory, together with datarepresenting EP measurements taken by EP electrodes corresponding to thetransducer locations. If, after the mapping basket 14 has been removedfrom the patient, the user wishes to guide an ablation catheter to alocation corresponding to one of the basket electrodes, s/he may electto display the saved location information for the basket simultaneouslywith the real time position of the ablation catheter.

The graphical user interface is further provided with several additionalfunctions that improve the accuracy and usefulness of the system.

For example, the microprocessor 112 includes software which enhances theaccuracy of the system by “gating out” the effects of cardiac motion onthe position data calculated for the transducers and/or catheters.Because a beating heart contracts and expands with each beat, thecatheter will move with the heart throughout the cardiac cycle even whena catheter is at a mechanically stable location within the heart. Thus,a real time display of the catheter (or transducer) position would showthe catheter or transducer moving on the display because of the cardiacmovement.

Such movement of the catheter/transducer on the display does not presentproblems in and of itself. However, if the user elects to save in thesystem memory the position of the catheter so that it may be used laterduring the procedure (such as to indicate anatomical landmarks, ablationlocations, mapping locations, etc.), the effects of the movement on thesaved locations can lead to inaccuracies if the user attempts tonavigate a catheter (shown in real time on the display) with respect tothe representation on the graphical display of the previous catheterposition data.

To eliminate this problem, the patient's electrocardiogram (EKG) ismonitored during use of the system, and the EKG is used to synchronizethe acquisition of position data so that all position data is acquiredat the same point in the cardiac cycle. Thus, for example, when EPsignals are recorded from catheters having integrated localizationtransducers, the relative position/location information for the EPelectrodes is accurate when displayed because all of the locationinformation will have been collected during the same phase of thecardiac cycle. Gating is similarly carried out for the ablation andmarking catheters, by collecting the appropriate position/location datafor such catheters and the anatomical landmarks during the same phase ofthe cardiac cycle.

FIG. 30B shows an EKG signal along with corresponding electrode positiondata recorded over the cardiac cycle. It has been found that the end ofdiastole, at the Q-R wave of the EKG signal, is a convenient point forgating the position measurements. FIG. 30A schematically shows a gatingsystem in which a patient's EKG signal is passed through an amplifier302 and a detector 304 which initiates a sample and hold sequence 306 ofposition data when the initiation of a Q-R wave is detected.

The user preferably has the option of showing the gated position, or theactual (moving) position, or both on the real time display. The actualposition of a catheter may be useful for assessing whether a catheter isin firm contact with the wall of the heart, because if the catheter isspaced away from the wall it will not move with the wall. A display ofactual position may also be helpful during steering of a catheterbecause it provides more rapid feedback of a catheter's position andorientation.

It should be emphasized, however, that gated position information isessential during navigation of a catheter to a location which has beensaved in the three-dimensional display, because unless the catheterposition and the stored location are gated to the same point in thecardiac cycle, the user cannot be certain that the catheter has beennavigated to the proper location.

Similarly, if EP signals are to be displayed in the form of anisochronal map on the three-dimensional display, the position used inthe isochronal map to display an activation time for that locationshould be an EKG gated location.

Similar gating may also be provided to eliminate inaccuracies inlocation information due to the rising and falling of the chest duringrespiration. For respiratory gating, chest movement would be monitoredusing a bellows or other device and the sample and hold sequence wouldbe triggered at a desired portion of the respiratory cycle.

Referring to FIG. 31, the gated positions of lesions and anatomicallandmarks may be stored in the system software and added and deletedfrom the display as needed by the user by manipulating a cursor using amouse or other user input device to the appropriate item in marker box156.

The microprocessor 112 is preferably further provided with softwarewhich allows the physician to manipulate the display in many ways sothat the maximum benefit may be obtained from the system. For example,referring again to FIG. 31, the user can rotate the display inthree-dimensions by guiding the cursor to the appropriate icon inmanipulation box 158. The user may likewise “zoom” towards or away fromthe image in the same manner. S/he may also elect which of the catheters10, 10 a, 12, 16 to display in real time using real time box 156.

The system further allows the user to select one of the standardorientations used in fluoroscopy such as anterior-posterior (“AP”),lateral, right anterior oblique (“RAO”) or left anterior oblique (“LAO”)by selecting the appropriate icon in orientation box 160. In the RAOview, the plane formed by the aortic-valve ring (“AV ring”) isapproximately perpendicular to the plane of the display, with the end ofthe coronary sinus pointing to approximately the 2-3 o'clock position onthe AV ring. In the LAO view, the apex of the heart is oriented suchthat it “points” towards a user viewing the display.

When the system of the invention is used is a preferred mode, thetransducers of a reference catheter positioned in the coronary sinus(“CS reference catheter”) define the AV ring, and the distal tip of asecond reference catheter is positioned in the RV apex (“RV apexcatheter”). The system can orient the display to an RAO orientation byderiving the location of the AV ring from the location of thetransducers on the CS reference catheter, and re-orienting the displayuntil the AV ring is perpendicular to the display and until the distaltip of the CS reference catheter points towards the 2 o'clock position.

With the AV ring perpendicular to the display, the system may alsodisplay straight anterior, posterior, left lateral, and right lateralviews by orienting the CS catheter distal tip at the 12 o'clock, 6o'clock, 3 o'clock, and 9 o'clock positions, respectively.

Similarly, the system can orient the display to an LAO orientation byderiving the location of the RV apex from the locations of thetransducers on the RV apex catheter, and by orienting the display sothat the RV apex points out of the display.

Operation

Two examples of procedures which may be carried out using the system ofthe present invention will next be described. It should be appreciated,however, that the system 100 may be utilized in any procedure in whichthree-dimensional navigation of devices relative to one another isrequired.

FIG. 33 is a flow diagram giving a sample methodology for using thesystem according to the present invention for diagnosis and treatment ofventricular tachycardia. The steps shown in the flow diagram will bediscussed with reference to the illustrations of the heart shown inFIGS. 34A through 34D.

First, step 200, a reference catheter 10 is introduced into the inferiorvena cava and is passed under fluoroscopy into the right ventricle(designated RV). The catheter is positioned with its distal tip at theapex (A). A second reference catheter 10 a is introduced via thesuperior vena cava into the coronary sinus (a vein, shown and designatedCS in FIG. 34B, that extends around the edge of the AV ring separatingthe left atrium and the left ventricle). The reference catheters may bepositioned elsewhere without departing from the scope of the presentinvention. However, the RV and CS are suitable locations because theyallow the catheters to remain mechanically stable within the heart.Moreover, these reference catheters will include the EP electrodesequivalent to those already used on CS and RV apex catheters, i.e. theywill replace conventional CS and RV apex catheters, Placement of thereference catheters using these approaches therefore does not requireintroduction of additional introducer sheaths or catheters into thepatient.

Throughout the procedure, the system calculates the relative positionsof the ultrasound reference transducers 18 (FIG. 3) using time-of-flightmeasurements and triangulation, establishes the three-dimensionalcoordinate system, and displays at least a portion of the referencecatheter on the graphical interface 124.

Next, referring again to FIG. 34A, marking catheter 12 is preferably(but optionally) introduced into the left ventricle. Catheter 12 isguided under fluoroscopy to sequentially position its distal tip againstvarious anatomical landmarks, such as the apex, septal wall, lateralwall, etc. The location of each transducer 34 (FIG. 9) relative to thereference catheters is calculated again using time-of-flightmeasurements and triangulation. The location of the catheter distal tipand thus the location of the anatomical site is extrapolated from thetransducer location using a model of the catheter 12 pre-programmed intothe system, and it may be subsequently displayed on the graphicaldisplay. Once the desired landmarks are identified and displayed, themarking catheter 12 is removed from the heart. Steps 202-208.

Referring to FIG. 34C, basket catheter 14 (FIG. 13) is next introducedunder fluoroscopy into the left ventricle (LV), at a location at whichthe clinician suspects there may be arrhythmogenic tissue. Step 210.Because the basket arms 52 include ultrasound transducers 58 as well asmapping electrodes 56, the locations of the mapping electrodes can bedetermined relative to the reference catheters and displayed on thegraphical display based on a model of the basket 50 programmed into thesystem. Step 212.

Electrical activity within the heart is recorded from the mappingelectrodes 56 and mapping data derived from the recorded activity isdisplayed on the graphical display. The EP signal display may bedisplayed separately from the three-dimensional display, such as in thesignal display window 162 shown in FIG. 32. Each graph in the signaldisplay window 162 represents the voltage data over time, as measured byone of the EP electrodes 56 on the basket catheter 14.

The EP signals may alternatively be displayed in the form of anisochronal map on the three-dimensional display. A display of this typewould be generated by first placing an activation time on each signal,where an activation time is the time at which the tissue under a mappingelectrode 56 activates. The activation times can be either placedautomatically using an algorithm or manually by the user. The map isgenerated by showing a color on the three-dimensional display thatrepresents an activation time at a location corresponding to thelocation of the electrodes that measured the signal. It may be in theform of discrete color dots or an interpolated color surface or sheetwhich passes through the locations of the EP electrodes.

The EP display may alternatively take the form of an isopotentialdisplay on the three-dimensional display. An isopotential map is similarto an isochronal map except that it is a time varying color display thatis proportional to signal amplitude rather than a static display ofactivation time.

Other mapping data derived from the EP signals may also be shown on thedisplay. For example, data indicating the adequacy of contact betweenthe electrodes and the tissue, or indicating the probability that thereis an arrhythmogenic site at the mapped location may be represented onthe display. The physician may induce electrical activity for subsequentmeasurement by pacing the heart from the basket electrodes 56. Step 214.

If an arrhythmogenic region is identified by the clinician on the visualdisplay, a marking and ablation catheter 12 (FIG. 9) is inserted intothe center lumen 80 of mapping catheter 14 (FIG. 15) and is guided intothe left ventricle. The three-dimensional position of the ablationelectrode 36 is displayed (using ultrasound receiving transducer 18 totrack its position) in real time to aid the physician in guiding theelectrode 36 to the arrhythmogenic region of the endocardium. FIG. 34Dand step 216. Once the ablation electrode is positioned at thearrhythmogenic region, ablation is carried out by supplying RF energy tothe electrode 36.

The clinician next attempts to induce ventricular tachycardia by pacingthe site from the basket catheter electrodes 56 or from electrodes onanother catheter. Step 220. If VT cannot be induced, the procedure isconsidered successful and the catheters 10, 14 are removed. Step 222. IfVT is induced, additional mapping and ablation steps are formed untilthe VT appears to be eradicated.

It should be noted that if mapping is carried out using a basketcatheter that is not provided with a center lumen 39, the basketcatheter may be removed after its electrode positions and correspondingmapping signals (which may include a visual identification of thearrhythmogenic region) are saved in the system memory, and a separateablation catheter may be introduced into the heart and guided to thearrhythmogenic region identified on a visual display of the gatedpositions of the mapping electrodes.

FIG. 35 is a flow diagram illustrating use of the system according tothe present invention with a linear lesion catheter of the type shown inFIGS. 18-26 to treat atrial fibrillation. The steps shown in the flowdiagram will be discussed with reference to the illustrations of theheart shown in FIGS. 36A-36C and the examples of the graphical userinterface shown in FIGS. 31 and 32.

First, reference catheters 10, 10 a are placed in the coronary sinus andRV apex as illustrated in FIGS. 34A and 34B. The reference catheters 10,10 a are preferably represented on the graphical display as shown inFIG. 31. Step 300. Although only the reference transducer positions areprecisely known, the catheter locations can be estimated using thetransducer positions, the known spacing of the transducers along thecatheter bodies, and a known model of the catheter.

Next, referring to FIG. 36A, marking catheter 12 (FIG. 9) is positionedin the left atrium, preferably by inserting it through a transeptalsheath passed from the right atrium, through the septum and into theleft atrium. Steps 302-304. Marking catheter 12 is sequentiallypositioned with its distal tip at anatomical landmarks, such as thepulmonary veins, septal wall, mitral valve, etc.

The location of each ultrasound transducer 34 on the marking catheter 12relative to the 3-D coordinate system is calculated using time-of-flightmeasurements and triangulation. The position of the distal tip isextrapolated from the transducer using a model of the catheterpre-programmed into the system, and is subsequently displayed on thegraphical display when the distal tip is positioned at a desiredanatomical site (as verified using fluoroscopy), the user adds anappropriate indicator to the display at the distal tip location byentering the necessary input at marker box 156 (FIG. 31). For example,see FIG. 31 in which the left inferior pulmonary vein, right superiorpulmonary vein, and right inferior pulmonary vein are identified as“LI,” “RS,” and “RI.” After the appropriate landmarks are added to the3-D display, the marking catheter 12 is removed from the heart.

Next, using a mouse or other user input device, lines representingtarget locations for linear lesions are added to the display. Step 312.These lines are identified by the dashed lines on FIG. 31. The linearlesion catheter 16 (FIG. 8) is next inserted into the left atrium,preferably via the transeptal sheath 87 shown in FIG. 36A. Duringplacement of the linear lesion catheter, the position of ablation window86 (FIG. 19) is tracked in real time by tracking the positions of thetransducers 92 using the localization system 100 and by deriving thewindow location from the transducer location. An arrow A1 or other iconrepresenting the length of the catheter 16 lying between the transducers92 is shown on the display as shown in FIG. 31.

Referring to FIG. 36B, lesion catheter 16 b (shown in FIG. 36B to havean ablation section slidable on a looped baffle wire as described inPCT/US96/17536), is guided using the localization system 100 to a firstone of the desired ablation locations marked onto the display by thephysician. By manipulating the catheter 16 such that the display showsarrow A1 lying over the area marked as a target location, the physiciancan ensure that the window 86 through which ablation will occur is atthe correct location. If a different type of ablation catheter is used,including one which does not involve the use of an electrolytic fluid,the physician may use a similar procedure to align the ablation section(which may be an electrode, an electrode array, or another region of theablation catheter at which ablation will be carried out) with the targetlocation.

RF energy is supplied to the RF electrodes 90 (FIG. 19) while aconductive fluid is supplied to the fluid port 96 (FIG. 18), to create alinear lesion in the target tissue. Step 318. Arrows A2 or other iconsrepresenting the window 86 positions during each ablation are added tothe display to indicate the location of a linear lesion. These arrowsmay be coded by color or other means to indicate characteristics of thelesion, such as the wattage used to create the lesion or the impedanceduring the ablation. The linear lesion catheter is then repositioned foradditional ablation steps until all of the desired ablation locationshave been treated.

Next, the linear lesion catheter is removed, and mapping basket 50 isinserted into the left atrium as shown in FIG. 36C. Steps 322, 324. Thepositions of basket electrodes and arms are determined using theultrasound localization system and are displayed on the 3-D display inthe manner described above. FIG. 32 illustrates the positions of thearms 52 with solid lines and the position of the recording electrodes 56with stars. Pacing and mapping is carried out using the electrodes 56 ina conventional manner to determine whether the linear lesions haveblocked transmission of the electrical currents that traverse the leftatrium during an atrial fibrillation episode. The electrical activitymeasured by the mapping electrodes 56 is shown in the form of anisochronal map over the lesion locations A2 on the three-dimensionaldisplay. Steps 328-330. If the linear lesions are found to besuccessful, the basket catheter is removed and the procedure ended. Ifadditional lesions are necessary, the locating, the ablating, pacing andmapping steps are repeated.

One embodiment of the system of the present invention has beendescribed, and it has been described primarily with respect to EPcatheters and cardiovascular procedures. It should be appreciated,however, that the system and its components may be used in a variety ofmedical and non-medical contexts in which three-dimensionalrepresentation of structures and surfaces is needed. Thus, the presentinvention is not to be limited by the specific embodiments andprocedures described herein, but should be defined only in terms of thefollowing claims.

We claim:
 1. A system for marking an anatomical structure, comprising:at least one reference element; a marking catheter configured for beingintroducing within an anatomical structure, the marking cathetercarrying at least one tracking element; localization hardware configuredfor causing the at least one reference element and the at least onetracking element to transmit and/or receive tracking signals betweeneach other; and a processor configured for determining positions of themarking catheter within a three-dimensional coordinate system based onthe tracking signals; and a graphical user interface configured forrecording one of the positions of the marking catheter, and forgraphically generating an anatomical landmark corresponding to therecorded position.
 2. The system of claim 1, wherein the at least onereference element and the at least one tracking element are ultrasoundtransducers.
 3. The system of claim 1, wherein the marking catheter isan intravascular catheter.
 4. The system of claim 1, wherein the markingcatheter carries a tissue ablative element.
 5. The system of claim 1,wherein the marking catheter carries a tissue mapping element.
 6. Thesystem of claim 1, further comprising a reference catheter carrying theat least one reference element.
 7. The system of claim 1, wherein thelocalization hardware is configured for causing the at least onereference element to transmit signals to the at least one trackingelement.
 8. The system of claim 1, wherein the at least one referenceelement comprises at least four reference elements, the localizationhardware is configured for causing the at least four reference elementsto transmit signals between each other, and wherein the processor isconfigured for establishing the three-dimensional coordinate systembased on the signals transmitted between the at least four referenceelements.
 9. The system of claim 1, wherein the processor is configuredfor determining positions of the least one tracking element within thethree-dimensional coordinate system based on the tracking signals, andderiving the positions of the marking catheter from the positions of theat least one tracking element.
 10. The system of claim 9, wherein thelocalization hardware is configured for measuring the elapsed timebetween the transmission and reception of the tracking signals, and theprocessor is configured for calculating the distances between the atleast one reference element and the at least one tracking element basedon the tracking signals, and determining the positions of the at leastone tracking element within the three-dimensional coordinate systembased on the calculated distances.
 11. The system of claim 9, whereinthe positions of the marking catheter are positions of a distal tip ofthe marking catheter.
 12. The system of claim 1, wherein the graphicaluser interface is configured for recording the position immediately inresponse to a user prompt.
 13. The system of claim 1, wherein thegraphical user interface is configured for graphically generating themarking catheter based on the determined positions of the at least onetracking element.
 14. The system of claim 1, wherein the graphical userinterface is configured for graphically generating an electricalactivity map of the anatomical structure based on the determinedpositions of the at least one tracking element.
 15. The system of claim1, wherein the graphical user interface comprises a display fordisplaying the graphically generated anatomical landmark.
 16. The systemof claim 1, wherein the graphically generated anatomical landmarkcomprises textual information.
 17. The system of claim 1, wherein thegraphical user interface includes a user input device, and wherein thegraphical user interface is configured for graphically generating theanatomical landmark in response to selecting one of a list of displayeditems via the user input device.
 18. A method of marking an anatomicalstructure, comprising: introducing a marking catheter within theanatomical structure; transmitting tracking signals between the markingcatheter and a reference element; determining positions of the markingcatheter within a three-dimensional coordinate system based on thetracking signals; recording one of the positions of the marking catheterimmediately in response to a user prompt; and displaying a graphicalanatomical landmark corresponding to the recorded position.
 19. Themethod of claim 18, wherein the tracking signals are ultrasound signals.20. The method of claim 18, wherein the marking catheter isintravascularly introduced into the anatomical structure.
 21. The methodof claim 18, further comprising ablating the anatomical structure withthe marking catheter.
 22. The method of claim 18, further comprisingelectrically mapping the anatomical structure with the marking catheter.23. The method of claim 18, further comprising introducing the referenceelement within the anatomical structure.
 24. The method of claim 18,wherein the positions of the marking catheter are positions of a distaltip of the marking catheter.
 25. The method of claim 18, furthercomprising displaying a graphical representation of the marking catheterbased on the determined positions of the marking catheter.
 26. Themethod of claim 18, further comprising displaying an electrical activitymap of the anatomical structure, wherein the graphical anatomicallandmark is displayed with the electrical activity map.
 27. The methodof claim 18, wherein the graphical anatomical landmark comprises textualinformation.
 28. The method of claim 18, wherein the anatomicalstructure is a heart.
 29. The method of claim 18, further comprisingnavigating one or more catheters within the anatomical structure basedon the displayed anatomical landmark.
 30. The method of claim 18,wherein the graphical anatomical landmark is displayed in response toselecting one of a list of displayed items via a user input device.